Gear pump with balanced side sealing bushes

ABSTRACT

A gear pump for fluids, comprising gears which are laterally sealed by a counter pressure as a function of the delivery pressure. Sealing gaskets pertaining to the counter pressure have cylindrical seats. Counter pressure limiting rings independent of the wall and of the gear sealing bush, yet firmly held against the wall by a mechanical surface seal as a function of the difference in the diameters of the rings, thereby guaranteeing constant adhesion on the part of the contact surfaces between the rings and the wall while the pump is in operation. The rings are placed asymmetrically with respect to the surface of the sealing wall, so as to displace the center of gravity of the counter pressure towards the delivery side and make it coincide with the center of gravity of the internal pressure on the sealing wall.

United States Patent [191 Menini GEAR PUMP WITH BALANCED SIDE SEALING BUSHES [75] Inventor: Corrado Menini, Bologna, Italy [73] Assignee: Lamborghini Oleodinamica S.p.A.,

Argelato (Bologna), Italy [22] Filed: Mar. 15, 1972 [21] Appl. No.: 234,788

[30] Foreign Application Priority Data l/l967 Kinnamon ..4l8/l32 l0/l969 Eckerle ..4l8/l32 Primary Examiner--Carlton R. Croyle Assistant Examiner-John J. Vrablik [57] ABSTRACT A gear pump for fluids, comprising gears which are laterally sealed by a counter pressure as a function of the delivery pressure. Sealing gaskets pertaining to the counter pressure have cylindrical seats. Counter pressure limiting rings independent of the wall and of the gear sealing bush, yet firmly held against the wall by a mechanical surface seal as a function of the difference in the diameters of the rings, thereby guaranteeing constant adhesion on the part of the contact surfaces between the rings and the wall while the pump is in operation. The rings are placed asymmetrically with respect to the surface of the sealing wall, so as to displace the center of gravity of the counter pressure towards the delivery side and make it coincide with the center of gravity of the internal pressure on the sealing wall.

3 Claims, 6 Drawing Figures PATENTEBJUM 1 1 I974 3.816042 GEAR PUMP WITH BALANCED SIDE SEALING BUSHES This invention relates to a hydraulic gear pump with a constant capacity according to a fixed number of revolutions.

It is designed in such a way as to offer the following basic advantages, some of which are already known and some of which are innovations:

the delivery remains almost constant as variations occur in the pressure and in the temperature of the fluid since the walls sealing the ends of the gears are hydraulically compensated and balanced.

the ring shaped rubber gaskets which serve to seal the fluid under pressure do not lose their shape since deformation of the parts subjected to high pressures does not in the slightest alter the gasket seats.

the coupling of the parts does not call for any constructional precision concomitancy or tolerances since the parts for compensation and balancing are independent and separate from each other despite the fact that during operation they are united hydraulically.

It is known that for the majority of pumps, their life span is a function of the duration of the sealing gaskets. Moreover, it is known that a reason for the deterioration of the gaskets is because of the modification, under pressure, of the actual gasket seats. Thus in the pumps, when going from lb/sq. in. to the maximum working pressure, cracks occur so that the gasket, sub jected to the maximum pressure stress, deforms into the cracks thereby bringing about at the same time, the rupture of the gasket concerned.

The purpose of this invention is to prevent any change in the seat of the gaskets, even when going from zero pressure to the maximum pressure; that is to say that even though deformations occur just as in other pumps, the deformations do not affect the seat of the gaskets.

The value of the invention is all the more noticeable since the above mentioned life span characteristics are obtained although the pump itself has all the other characteristics for compensation and balancing for sealing the gears. To be more precise, the gear pump to which the invention refers is designed in such a way that the parts which serve to seal the gears are hydraulically balanced and although this is also done for other conventional pumps, the procedure for the pump forming the subject of the invention differs from that used for the pumps since the balancing is achieved through methods which prevent the gasket seats from undergoing any variation and thus the gaskets themselves from breaking.

The principle of the gasket seats not being deformed is based on the fact that solely cylindrical seats are fitted for balancing.

It is in fact known that a free cylindrical coupling (hole-shaft) can be achieved without difficulty with the minimum play necessary for the satisfactory operation of the gaskets. A characteristic of the invention is that there is eccentric balancing with the seal between the gear support bushes and the body of the pump being realized exclusively with elements of a cylindrical shape.

FIG. 1 shows a longitudinal section of the pump taken along the lines 1 l of FIG. 2. FIG. 2. provides a front view of the pump minus its cover but with its balancing rings. FIG. 3 provides a view of the pump minus its cover, base and its front sealing bush. FIG. 4

depicts a sectional detail of FIG. 1 showing the gasket and of the relevant balancing ring. FIG. 5 is a fragmentary front view of FIG. I with the cover and rings removed and shows a plan view of a seal. FIG. 6 is a fragmentary section taken along the lines 6 6 of FIG. 5 and illustrates the latter seal.

On FIG. 1 all the parts belonging to the pump are shown. The driving gear 1 takes its motion from the hub 2 and is supported by the front bush 3 and by the rear bush 4. The driven gear 5 is also supported by the above mentioned bushes 3 and 4, respectively. Both the gear assemblies I and 5 and the bushes 3 and 4 are housed in the pump body 6.

The hole in the body 6 which houses the gears and the sealing bushes is shaped like a figure 8, as can be seen from FIG. 2. The profile of the hole is the same as that of the two gears which mesh together.

The gear support bushes 3 and 4 also serve to seal the ends of the gears l and 5 and since the bushes oscillate on the hubs of the gears, they are thus able to remain firmly attached to the planes 7 and 8 of the gears. Again on FIG. 1, notice should be taken of the base 9 used to seal the rear side of the pump body and of the cover 10 used to seal the front side of the pump body. Both the base and the cover are fastened to the body by means of screws which are not shown on the drawing.

The base 9 has a through hole 11 and this is provided with an oil retainer 11b. The driving shaft slots into the former.

It can be seen from FIG. 3 that when the two gears are rotated in the directions indicated by the arrows l2 and 13, the fluid is carried into the pump through the inlet port 14 and it goes into and fills the spaces between the teeth of the two gears prior to being pushed through the pressure orifice 15. It is obvious that in order to reach high pressures there must necessarily be a perfect seal in the following places:

on the planes 7 and 8 (FIG. 1) between the gear ends and the support bushes 3 and 4;

- between the ends of the teeth and the pump body at points 16 and 17 (FIG. 3);

from point 18 to point 19 right along the perimeter on the inlet side of the bushes 3 and 4 between the bushes and the body (FIG. 2). In practice it is necessary for there to be full isolation between the pressure side and the inlet side.

While the seal between the tip of the teeth and the body is guaranteed bythe pressure which keeps the gears moved towards the inlet (FIG. 3) and the same can be said for the two bushes (3 and 4), it is instead necessary for a longitudinal thrust to be created in the direction 20 (FIG. I) in order to guarantee the seal on the planes 7 and 8.

It is known that this longitudinal thrust which holds the bushes 3 and 4 up against the gears is obtained by means of a hydrostatic communicating passage between the delivery area and the outer surface of the sealing bushes 3 and 4 (FIG. 1).

In this specific case, the counter pressure" is only applied to the bush 3 in the direction 20 on the side of the cover 10 (FIG. 1) and this provides a thrust and reaction sealing efie'ct on the planes 7 and 8.

What has been defined as counter pressure is in reality the pressure which is created between the cover 10 and the bush 3 (FIG. 1) on side 22, as a result of 23 communicatingwith the pressure orifice (FIG. 2).

The bush 3 (FIG. 1), like a wall, is therefore subjected to hydrostatic pressure on both sides. The inner side 7, that is to say the one which touches against the sides of the gears, is subjected to a non-uniform pressure distributed over its surface which in fact will be nil on the side where the inlet port 14 (FIG. 3) is located and at its most on the pressure orifice 15 side. For major clarity, FIG. 3 has dotted lines to show the surface of the bush 3 subjected to internal pressure.

It is obvious that the centre of gravity 21 (FIG. 2) resulting from the internal pressure does not lay across the symmetrical axis of the bush and that it will instead by displaced to a certain extent towards the outlet port 15 (FIG. 3).

In order therefore that the bush be balanced prefectly, it is necessary for the centres of gravity for the pressure on both the sides 7 and 22 to be in alignment with each other and for the resultant of the counter pressure to be equal to or slightly greater than the resultant of the internal pressure.

Leaving unchanged the distribution of the pressure on the inner side 7 of the bush and, in consequence, also the resulting force in the opposite direction to on the bush and the relevant centre of gravity 21, action must be taken with the distribution of the counter pressure so that the previously mentioned condition of perfect balance be respected. This is done by dividing the external surface 22 of the bush 3 into two parts: one subjected to pressure through the connection 23 with the pump delivery and the other not subjected to pressure by connecting it to the inlet of the pump. This connection is not shown on the drawing.

The size, the shape and the position of these two parts determine the value and the centre of gravity of the resultant of the counter pressure.

Various conventional systems are used to delimitate these two parts and they can be divided into two categories:

1). slots are made in the cover and the gaskets fit into them; the perimeter of these slots is designed in a special way in order to create pressure and vacuum areas for the bushes; this system has the great fault of causing the gaskets to break since their seating slots in the cover are subject to becoming misshapen towards the outside of the cover whilst it is being subjected to pressure and also because of the inward movements of the bushes; these two movements alter the gasket seat and tend to create a gap between the bush and the cover into which the gasket extrudes and damages itself;

2. the figure eight shaped sealing bush has two hubs forming an integral body with the actual bushes and these hubs act as pistons and are housed in two cylindrical compartments machined into the cover; the pistons create, with the addition of gaskets, two circular areas to which pressure is not applied; naturally when the pistons are suitably dimensioned, the counter pressure on the figure eight shaped bushes can be established; although this system does not have the same fault as those belonging to the first category, since the cylindrical seat of the gaskets does not suffer from deformation, it does present enormous difficulties both for the balancing of the figure eight shaped bushes and for the assembly operation which requires absolute precision between the centres of the bushes housed in the body and the centres of the pistons located in the cover.

The novel solution adopted for this particular invention amalgamates the advantages of having a seat which definitely cannot lose its original shape with those of greater manufacturing ease and perfect balancing.

On this type of pump the delimitation of the areas is in fact achieved through two identical rings 24 and 25 resting on the respective figure eight shaped bush 3 (see FIGS. 1 and 4 one of the two rings 24 and 25 is shown enlarged on the latter figure). Each ring is provided with an edge 26 (FIG. 4) which rests on the surface 7 of the bush and delimitates the two areas (pressure 27, vacuum 28). Because of the difference in its diameters (lower 29, upper 30), the ring is pushed by the pressure of the fluid against the bush 3 (FIG. 4) in such a way that it can be guaranteed that the ring remains firmly attached to the bush and thus when the latter is subjected to pressure, they form together one integral body. As seen above, the ring 24 (FIG. 4) slides with its diameter 29 inside runners machined in the cover. The position of the runners for the rings 24 and 25 is left loose since they do not constitute one integral body with the bush and thus the only precise machining operations are those for the diameter of the runner and of the ring. Should the bush eventually sink, it would not affect the rings or their seats because as has already been seen, the rings rest on and thus can slide on the bushes themselves. The ring 24 and the seat in which it slides longitudinally form the seat for the gasket 31 (FIG. 4). Between the ring and the seat there is a minimum play which does not vary with the operating conditions and this prevents the seat from becoming misshaped or the gasket 31 placed in the free area between the ring and the seat from being extruded. Furthermore, as can be seen from FIG. 2, these rings are not symmetrical with respect to the bush but are displaced by a quantity 32 which is such that the centre of gravity of the counter pressure is aligned with the centre of gravity 2] of the internal pressure (FIG. 3) and (FIG. 2).

In order to complete, following the same procedure, the isolating seal between the pressure side and the vac-. uum side of the pump, a third gasket 33 (FIGS. 5 & 6), again cylindrical, is used and this guarantees the perimeter seal from point 18 to point 19 (FIGS. 2-5). It is in fact difficult to achieve, from a seal point of view, the coupling of the bush 3 to the body 6 at the point 34 where the two circumferences forming the profile of the bush (FIG. 5) meet. Although from the pressure orifice side 15 this particular seal is not required, it is necessary to create a gap 23 in order to communicate with the known counter pressure (FIG. 2), while from the inlet side it is indispensable for there should not be any fluid passing along the perimeter from 18 to 19 or between the counter pressure and inlet zones. With this particular type of pump, the section 34 where the two circumferences meet has been replaced, on the inlet side, with a cylindrical element 35 placed inside a hole which serves both for the figure eight shaped bush 3 and for the body 6. FIG. 5 shows the cylindrical element 35 with the gasket 33 housed in a hole, a half of which 36 is in the bush 3 and the other half of which 37 is in the body 6. On one end of the element 35 a reduced portion 35a defines an annular space 35b in operative communication with the inlet and in operative communication with the low pressure side of the bal ancing rings, as indicated by dashed lines 35c in FIG. 1

a body having a recess and on one transverse side a low pressure inlet and the other transverse side a high pressure outlet orifice, communicating therewith,

cooperating gears disposed in said recess,

gear sealing bushes laterally sealing each side of said gears in symmetrical relation thereto,

counter pressure annular balancing rings independent of said sealing bushes and disposed against one side of one of said sealing bushes,

said balancing rings each having two different diameters and form a sealing seat,

an annular ring sealing gasket disposed about each of said balancing rings in said sealing seat,

a communicating connection communicating said high pressure outlet with one side of said balancing rings, the other side of said balancing rings communicating with said inlet, said balancing rings pressing laterally against said one sealing bush firmly as a function of the difference in diameters of said balancing rings, insuring constant adhesion of said balancing rings against said one sealing bush when said pump is in operation, and

said balancing rings being asymmetrically oriented with respect to said gears in a direction toward said one transverse side closer toward said inlet, such that said balancing rings exert counter pressure against said one sealing bush coinciding with an internal pressure in said gears against the other side of said one sealing bush, obtaining a center of high pressure displaced in a direction toward said other transverse side closer to said outlet orifice,

said recess has the shape of a figure eight,

a cylindrical means disposed in a transverse opening formed partially in the sealing bush between said gears and said balancing rings and partially in said body, at a narrowed portion of the figure eight shape adjacent said inlet forming thereat a seal against operative communication between said inlet and said high pressure.

2. The pump, as set forth in claim 1 wherein said cylinder means comprises,

a cylindrical element having first and second reduced portions and a center portion therebetween, the latter complementarily disposed in said opening,

said first reduced portion defines with said opening an annular space in operative communication with said inlet, and

a ring gasket disposed about said second reduced portion and abutting said opening.

3. The pump, as set forth in claim 1 wherein said communicating connection communicating said high pressure outlet side with said one side of said balancing rings is adjacent the other narrowed portion of said figure eight shape adjacent said outlet.

i UNl TED STATES PATENQI OFFICE CERTIFICATE OF CORRECTION patent 5,816,042 Dated June 11, 1974 Corrado Menini Inventor(s) v It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet [73] "Argelato (Bologna); Italy" should read Funo Argelato (Bologna) Italy item [30] "3369/71" should read 3369 A/71 Signed and sealed this 5th day of November 1974.

(SEAL) Attest C. MARSHALL DANN McCOY M. GIBSON JR. Attesting Officer Comissioner of Patents uscoMM-oc 00316-1 U,$. GUVERNMENT PRINTING OFFICE:

F ORM PO-I 050 (10-69) 

1. A compensated and balanced gear pump for fluids, comprising a body having a recess and on one transverse side a low pressure inlet and the other transverse side a high pressure outlet orifice, communicating therewith, cooperating gears disposed in said recess, gear sealing bushes laterally sealing each side of said gears in symmetrical relation thereto, counter pressure annular balancing rings independent of said sealing bushes and disposed against one side of one of said sealing bushes, said balancing rings each having two different diameters and form a sealing seat, an annular ring sealing gAsket disposed about each of said balancing rings in said sealing seat, a communicating connection communicating said high pressure outlet with one side of said balancing rings, the other side of said balancing rings communicating with said inlet, said balancing rings pressing laterally against said one sealing bush firmly as a function of the difference in diameters of said balancing rings, insuring constant adhesion of said balancing rings against said one sealing bush when said pump is in operation, and said balancing rings being asymmetrically oriented with respect to said gears in a direction toward said one transverse side closer toward said inlet, such that said balancing rings exert counter pressure against said one sealing bush coinciding with an internal pressure in said gears against the other side of said one sealing bush, obtaining a center of high pressure displaced in a direction toward said other transverse side closer to said outlet orifice, said recess has the shape of a figure eight, a cylindrical means disposed in a transverse opening formed partially in the sealing bush between said gears and said balancing rings and partially in said body, at a narrowed portion of the figure eight shape adjacent said inlet forming thereat a seal against operative communication between said inlet and said high pressure.
 2. The pump, as set forth in claim 1 wherein said cylinder means comprises, a cylindrical element having first and second reduced portions and a center portion therebetween, the latter complementarily disposed in said opening, said first reduced portion defines with said opening an annular space in operative communication with said inlet, and a ring gasket disposed about said second reduced portion and abutting said opening.
 3. The pump, as set forth in claim 1 wherein said communicating connection communicating said high pressure outlet side with said one side of said balancing rings is adjacent the other narrowed portion of said figure eight shape adjacent said outlet. 